The development of new methods for increasing the biological activity of agricultural insecticides is an active field of research. Researchers in this field endeavor to develop new combinations of insecticidal compositions, e.g., mixtures of insecticidal compounds with other known agricultural ingredients, mixtures of insecticidal compounds with synergistic compounds and the like, having enhanced biological activity in comparison with the combined additive biological activity of the individual components thereof. U.S. Pat. No. 4,173,637 and U.S. Pat. No. 3,748,356 teach that mixtures of the insecticidal compounds described therein, e.g., substituted benzoyl urea compounds, with other known agricultural ingredients may produce synergistic effects. Several articles report the use of synergistic compounds, e.g., phosphorous-containing compounds, which may enhance the toxicity of insecticidal compounds in combination therewith. See Plapp Jr., Bigley, Chapman and Eddy, Journal of Economic Entomology, Vol. 56, No. 5, 1963, pages 643-649; Attia, Shenahan and Shipp, Journal of Economic Entomology, Vol. 73, No. 2, 1980, pages 184-185; and Pimprikar and Georghiou, Pesticide Biochemistry and Physiology, Vol. 12, No. 1, 1979, pages 10-22. This field of research is important not only for fulfilling such important objectives and eliminating undesirable insects, combatting a wide variety of insecticide-resistant insects, enhancing the harvested quantity of crops and the like, but also from an economic and environmental point of view in reducing the amount of active ingredient normally required for the particular application.
However, researchers have found that synergistic insectidal activity can only be positively determined by experimentation. Certain combinations of insecticidal compositions, e.g., mixtures of insectidical compounds with other known agricultural ingredients or mixtures of insecticidal compounds with known synergistic compounds at specified concentration amount, may unexpectedly exhibit no synergistic activity whereas other combinations of insecticidal compositions at the same concentration amounts may unexpectedly exhibit synergistic activity. Surprisingly, as a result of extensive research in the development of new methods for increasing the biological activity of agricultural insecticides, the present invention provides chewing insect toxicant compositions comprising a 1-(mono-substituted phenyl)-3-benzoyl urea compound in admixture with a phosphorous-containing compound as structurally depicted below. These compositions have greatly enhanced biological activity on chewing insects in comparison with the combined additive biological activity of the 1-(mono-substituted phenyl)-3-benzoyl urea compound alone and the phosphorous-containing compound alone at specified concentration amounts.